JSX
JSX is a templating language created by React team. It's just a syntactic sugar for the below React JSX Factory Function.
React.createElement(component, props, ...children);
This means that the compiler converts JSX to JS by adding React.createElement function.
import React from 'react'; // We need this import. Otherwise the compiler will not add it.
function App() {
return <h1>Hello World</h1>;
}
After compiling, the JSX would look as below.
import React from 'react';
function App() {
return React.createElement('h1', null, 'Hello world');
}
React.createElement isn't for generating HTML elements. It's only for converting JSX to JS.
Using the new 'react/jsx-runtime'
The old way of using React.CreateElement had a problem of having React in the import always and also this method had some performance problems.
So jsx-runtime was introduced and this compiles JSX to the below JS code.
// Inserted by a compiler (don't import it yourself!)
import { jsx as _jsx } from 'react/jsx-runtime';
function App() {
return _jsx('h1', { children: 'Hello world' });
}
Tools used for compiling
Babel
Babel compiler can be used to compile JSX to JS as described above.
TypeScript
If using typescript, then JSX file are written as TSX files.
The tsconfig.json has a configuration to say which way must be used for compiling TSX to JS.
The configuration parameter jsx can be react to compile to createElement or react-jsx to compile to use 'react/jsx-runtime' library.
Why JSX
Generating HTML directly using plain JS is very error-prone and cumbersome. Example - matching open/close tags, escape content, etc. It's not only tough to write but also to read the code.
JSX has an HTML/XML based syntax. But it has nothing to do with HTML. But this makes it easy to write and understand.
It also provides the advantage where we can write pure/plain HTML directly in it and also co-locate the String interpolation in the same place.
On compilation, it will generate a JS script which will in-turn generate the HTML block for that component.
JSX doesn't directly create the HTML output. It only creates JS which is capable for generating the HTML.